Thermionic tube



Nov. 29, 1932. F. s. MCCULLOUGH 1,889,449

THERMIONIG TUBE Filed Nov. 24, 1926 ENTOR Patented Nov. 29, 1932 UNITED STATES FREDERICK S. MCCULLOUGH, OF EDGEWOOD, PENNSYLVANIA THERMIONIG TUBE Application filed November 24, 1926. Serial No. 150,546.

This invention relates to thermionic tubes andvmore particularly to hot cathode tubes.

of the three element type having in addition to the cathode, a grid or control electrode and a plate or anode.

In certain forms of thermionic tubes, and more particularly radio tubes as originally developed, the plate or anode was located on one side of the filament only and the grid was interposed between the filament and the plate. In standard tubes of present construction, the grid entirely surrounds the filament, and the plate entirely surrounds the grid. By reason of the relatively large area of the grid with respect to the plate, there is a very considerable capacity coupling between the grid and the plate. This so called internal capacity is objectionable in certain circuits employing radio tubes for the reason that self oscillation or regeneration takes place which it is diificult to control, and in neutralizing the tendency toward self oscillation, the efiiciency of the circuit is reduced. High internal capacity also has a tendency to reduce the selectivity of the circuit because of the fact that potentials impressed on the grid are transferred to the plate without amplification.

According to the present invention, it is proposed to provide a tube which shall have substantially the same characteristics of the present standard tube, but wherein the internal capacity is relatively low.

The nature of the invention may be readily understood by reference to the accompanying drawing which illustrates one embodiment of my invention and in which Figure 1 is a side elevation partly in section, showing more or less diagrammatically a tube constructed in accordance with my invention;

Figure 2 is a transverse section in the plane of line IIII of Figure 1.

In the drawing, 2 designates the base of a tube, 3 is the outer envelope and 4: is the stem.

In the base are the usual contact pins 5.

Supported in the'stem 4 is a post 6 having metal bands 7 secured thereto at spaced apart points. Fitted within the bands 7 is a tube or sleeve 8 which is preferably composed of a 0 non-conducting material, especially a heat resisting material, such as glass, porcelain or the like. Inside the tube 8 is a grid 9 which is supported on a post 10 mounted in the stem 4 in the usual manner. Passing up through the grid is a filament 11 having its lower end connected to a post 12 and its upper end connected to a support 13. Inside the tube 8 and at one side of the grid and filament is an anode 14: which ispreferably in the form of a narrow strip of metal extending vertically up one side of the tube; The anode is carried on a post 15.

In this construction, the grid entirely surrounds the filament so that it exerts an influence on the entire electron stream emitted from the filament. The non-conducting cylinder 8 forms a collector for electrons and confines them to the space immediately surrounding the electrodes of the tube. Being formed of a non-conducting material, this 7 collector does not have any appreciable affinity for the electrons, and merely confines them so that the majority of them will be attracted toward the plate.

By reason of the fact that the grid entirely surrounds the filament, the grid will exert an influence corresponding to the action at the grid in a standard tube. By reason of the small area of the plate or anode with respect to the grid, the internal capacity of the tube is extremely low. At the same time, due to the fact that the grid'entirely surrounds the cathode and due to the fact that the electrons are confined by the sleeve 8, the tube has substantially the same mutual conductance, amplification characteristics and plate current as a standard tube having a corresponding extent of filament.

While I have illustrated and described one particular embodiment of my invention, it will be understood that the invention may be otherwise embodied and that various changes and modifications may be made therein within the scope of the following claims.

I claim:

1. A thermionic tube comprising a sleeve formed of insulating material, a cathode inside the sleeve, a grid inside the sleeve substantially enclosing the cathode, and an anode in the sleeve outside the grid, the surface area 100 of the anode being considerably less than the area outlined by the grid.

2. A thermionic tube comprising a sleeve formed of insulating material, a cathode in the sleeve, a grid substantially enclosing the cathode, and a plate outside the grid and inside the sleeve, said anode comprising a narrow strip of conducting material extending longitudinally of the sleeve.

In testimony whereof I have hereunto set my hand.

FREDERICK S. MOGULLOUGH. 

